Increasing normal modes analysis accuracy: The SPASIBA spectroscopic force field introduced into the CHARMM program

In the present work, the SPASIBA spectroscopic force field has been introduced into the CHARMM program. The SPASIBA force field combines the van der Waals and electrostatic interactions as originally found into CHARMM with Urey-Bradley-Shimanouchi terms for bond stretching, valence angle bending, torsional and improper torsional internal coordinates. SPASIBA has a vibrational spectroscopic origin, and it has largely proven its efficiency in reproducing experimental data such as vibrational wavenumbers, dipole moments, rotational barriers, conformational energy differences, and moments of inertia. The SPASIBA parameters have been included into CHARMM by way of a particular library which directly activates calculations of the specific energetic terms.